Despite how it made you feel you made the right choice not to intervene. Be a good witness, take a photo/video of the car and thief and provide it to the store employee or LE.
This situation is a no win for you because of all the unknowns.
First, depending on where you live even if they are caught they will more likely than not only receive a criminal citation instead of a trip to jail. If they did go to jail, again depending on where you live more likely than not because it is only a misdemeanor theft they would be book and released from jail with a future court date. Again, depending on where you live the local DA may not even prosecute because the case loads are so high it is not worth their time.
Secondly, if you are dealing with a legit bad dude and not some run of the mill shoplifter they probably have been through much worse situations than you confronting them. Guys with nothing to lose are extremely dangerous and don’t give two craps about you or anyone else in society. They are also likely armed and would take extreme measures for self preservation.
Say you did intervene and you stop the theft, guy goes to jail, and the store gets their stuff back, great. You may get a thank you for your efforts and you will probably feel like you made a difference for that moment, but in the grand scheme of things it really does make zero difference in society overall.
Now let’s play devils advocate to the situation, you confront the guy and a fight ensues. You pull your carry piece because now your in a fight for your life and shoot him. Guess what, you will more likely than not get sued by him or his family and possibly lose everything you’ve worked for. And they may likely win because you interjected yourself into the situation.
Or say he pulls first and you are severely injured or killed, leaving your wife without a husband and your kid without a dad. All for a shoplift.
If you want societal changes made you have to make the changes at a higher level than on the street.
Your intentions are spot on to jump in if someone is in danger of injury or loss of life, but for things like a shoplift just be a good witness. Sorry for the long response, rant over.